Begell House Inc.
Multiphase Science and Technology
MST
0276-1459
19
1
2007
A MATHEMATICAL MODEL FOR TWO-PHASE STRATIFIED TURBULENT DUCT FLOW
1-48
10.1615/MultScienTechn.v19.i1.10
D.
Biberg
Scandpower Petroleum Technology, P.O.Box 113, Gåsevikvn. 2-4 N-2027 Kjeller, Norway
An algebraic-logarithmic model for two-phase stratified turbulent channel flow is presented. The various aspects of the model compare favorably with a wide range of data from the literature. The model is characterized by its ability to reproduce the effect of interfacial waves and momentum transfer, associated with large pressure drop increases in stratified flows. Its analytic nature allows for the derivation of relatively simple preintegrated (integrated analytically prior to run time) expressions for the mean wall and interfacial friction. The corresponding pipe flow expressions, ideally suited for 1-D computer models, are obtained by hydraulic similarity. The pipe flow friction formulae open up for the simulation of large pipeline systems with the consistency and accuracy of a cross sectional description, while maintaining the evaluation speed of a 1-D model. The work described in this article was motivated by the multiphase flow challenges met in the development of gas-condensate fields like Ormen Lange and Snøhvit on the Norwegian continental shelf.
THE PREDICTION OF FLOW PATTERN MAPS IN MINICHANNELS
49-73
10.1615/MultScienTechn.v19.i1.20
Amos
Ullmann
School of Mechanical Engineering,
The Iby and Aladar Fleischman Faculty of Engineering, Tel-Aviv University, Ramat Aviv 6139001, Israel
Neima
Brauner
School of Mechanical Engineering, Faculty of Engineering, Tel-Aviv University, Ramat Aviv 6139001, Israel
Commonly used models for predicting the flow patterns and flow pattern transitions are established for gas-liquid flows in normal-size channels (D > 0.5′′). Those are generally found to predict poorly experimental two-phase flow pattern data in minichannels. In this study, the effect of the channel diameter on the mechanisms leading to flow pattern transitions are reexamined in an attempt to identify the governing phenomena involved in two-phase flow in small-diameter channels. Accordingly, appropriate mechanistic models are suggested and compared with experimental flow pattern maps available from the literature. These models also indicate the controlling dimensionless groups and the critical values associated with the various flow pattern transitions. The analyses also suggest criteria, in terms of dimensionless Eotvos number, EoD, that indicate when the conventional models must be substituted with the minichannel models. The reasons for the disappearance of the stratified flow in mini- and microchannels are elaborated, and the various mechanisms leading to the establishment of annular flow as the basic flow pattern in low EoD systems are discussed.
OPTICAL MEASUREMENTS TO CHARACTERIZE TWO-PHASE FLUID FLOW IN MICROCHANNELS
75-97
10.1615/MultScienTechn.v19.i1.30
R.
Revellin
Laboratory of Heat and Mass Transfer, Ecole Polytechique Fédérale de Lausanne, Station 9, CH-1015 Lausanne, Switzerland
John R.
Thome
Laboratory of Heat and Mass Transfer (LTCM), Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 9, CH-1015 Lausanne, Switzerland
An extensive experimental two-phase flow study has been carried out on two single round tubes (D = 0.509 and 0.790 mm) for R-134a and R-245fa. The present paper summarizes our recently published results from this work. First of all, an optical measurement method for two-phase flow pattern characterization in microtubes was developed in order to determine the frequency of bubbles exiting a microevaporator, their coalescence rates, and lengths as well as their mean two-phase vapor velocity. Based on the bubble frequency results and CHF measurements made on the microevaporator (predicted with a new microchannel version of the Katto-Ohno correlation), a new type of flow pattern map for evaporating flow in microchannels was proposed with (i) an isolated bubble regime, where the bubble generation rate via nucleation in the microevaporator is much larger than the bubble coalescence rate and includes both bubbly and slug flows, (ii) a coalescing bubble regime, where the bubble coalescence rate dominates the bubble generation rate and exists up to the end of the coalescence process, (iii) an annular regime, which is a completely coalesced flow, and (iv) a mist flow regime, whose onset is indicated by the critical vapor quality corresponding to the critical heat flux (CHF). This flow pattern map may in the future be used as the starting point for the development of heat transfer and pressure drop models and the thermal design of microevaporators. In addition, an extensive new two-phase pressure drop database was obtained whose homogeneous friction factors versus Reynolds numbers fell into the well-recognizable laminar, transition, and turbulent flow regimes similar to those of the Moody diagram observed in single-phase flow.